1. Technical Field
The present invention relates to extracting characteristics of electrical signals for integrated circuit devices, and more particularly measuring switching speed, transition states and times between the transition states of the integrated circuit devices using optical techniques.
2. Description of the Related Art
It is very difficult to have access to electrical signals inside Integrated Circuits (IC) with conventional testing techniques. High numbers of metal layers, ultra-scaled dimensions of transistors and interconnections and flip-chip packages all prevent known testing methods from non-invasively measuring the internal electrical signal characteristics.
Picosecond Imaging Circuit Analysis (PICA) permits the testing of internal signals through the spontaneous emission originating from the switching activity of metal oxide semiconductor (MOS) transistors, collected from the backside of the circuit. However, the direct non-invasive measurement of the slew rate (i.e., the slope) of electrical signals is still not possible with PICA or other non-invasive conventional methods.
Several conventional testing techniques can measure the electrical signals inside integrated circuits, but all of these techniques are either invasive or cannot access all the signals. Mechanical testing makes use of mechanical probes to directly measure the electrical signals from chip interconnections or from dedicated test pads. The main drawbacks include invasiveness (e.g., mechanical probes cause a capacitive and resistive load of circuit nodes and perhaps physical damage). The mechanical probing can be used only for the top-level metals of the chip.
Electron Beam Tester (EBT) can analyze electrical signals inside an integrated circuit (IC) thanks to a scanning electron beam. The limitations for EBT include limited access to only the top-level metals of the chip and the inferior time and amplitude resolutions, which do not permit extraction of quantitative information regarding the slew rate of electrical signals.
Laser Voltage Probe (LVP) can access the signals from the backside of the chip but the laser invasiveness prevents the applicability of this technique to SOI (Silicon-On-Insulator) technologies. Moreover, the amplitude resolution is not sufficient for accurate slew rate estimations.